Active RFID tags can be used to provide perimeter protection. Patients and objects with active RFID tags may be unable to leave such a protected perimeter because a system can detect the presence of the tag and prevent a person bearing the tag from exiting the perimeter (for example, by engaging door locks and employing audio-visual alarms). For such applications, it is important to ensure that the tag cannot be removed from the patient or object without the system detecting such removal. It is also important to provide that tags can be secured to objects having unusual shapes, for example objects that do not have a flat surface.
There are available methods to address the removal of an active RFID tag from a patient. Two such methods are cut-band technology and capacitance sensing technology.
An example of tamper detection based on band conductivity is cut-band technology, which uses an electrically conductive band to secure a tag to a person's wrist, ankle or calf. The tag monitors whether the band is severed by detecting the resistance between two electrodes that are connected by the conductive band. There are several limitations to cut-band technology, for example it is difficult and expensive to manufacture a tag employing the technology, and it is relatively easy to remove such a tag, including the band, from a person's wrist or ankle without cutting the band. Therefore such a removal would not trigger a message that the tag has been tampered. This risk may be of particular concern if the tag is being used to monitor a newborn infant that happens to lose weight after birth. The use of cut-band technology may also result in false alarms due to inconsistencies in the ability to reliably detect the attachment of the band to the tag. Also, cut-band technology can be defeated by bypassing the band using a conductor with alligator clips on both ends.
Capacitance sensing technology includes a sensor within a tag capable of detecting a change in capacitance when it is either placed on a patient's body, or removed away from the body. This technology has several limitations, including that the change in capacitance is very small, and therefore may give rise to false alarms when the tag is not in proper contact with the person. It is also difficult and expensive to manufacture a tag with the capability of consistently detecting such small changes in capacitance.
Another solution available, for determining tampering of tags placed on objects, is the use of a mechanical solution in a form of a metal pin, protruding through the bottom of the tag enclosure, which opens or closes an electrical contact within the tag whenever it is removed or placed on the object.
A further problem with some of prior art tag tamper-detection methods are that they do not allow the tag enclosures to be fully sealed, because of the connectivity requirements between the internal tag electronics and any external sensors.
An existing solution to the problem of attaching active RFID tags (or tag holders) to surfaces include applying double-sided tape to keep the tag attached the object.